Tectonic evolution and sequence filling patterns in the western Sichuan foreland-like basin in the Upper Triassic Xujiahean period
Tectonic evolution and sequence filling patterns in the western Sichuan foreland-like basin in the Upper Triassic Xujiahean period
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发表时间：
2008
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通讯作者：
Zheng Rong-cai
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作者：
Zheng Rong-cai
龙门山构造活动在上三叠统须家河期具有明显的阶段性变化。须家河组二、四段沉积阶段与龙门山逆冲推覆阶段相吻合。川西前陆盆地的沉积中心和沉降中心位于盆缘冲断带附近的前部，盆地两侧储集层发育，沉积极不对称。随着龙门山造山带构造活动的加强，下切向侵蚀加剧，盆缘逆冲一侧的低位体系域较发育。而高水位体系域由于后期的陆上暴露和侵蚀而保存不完整。另一方面，前隆起斜坡一侧以稳定缓慢的隆升和弱的下切侵蚀为标志，低水位体系域不发育或不发育，后期侵蚀较弱，高水位体系域较发育。须家河组三段和五段沉积阶段恰逢龙门山冲断的休止期，川西类前陆盆地的沉积中心和沉降中心向前凸起方向移动；盆地两侧沉积不对称程度较低，以区域盖层和烃源岩发育为特征，两个阶段的层序充填模式与逆冲阶段相似，但造山带前部的沉积层序，特别是高位体系域，由于构造剥蚀作用较弱，保存完好；而前隆起的层序相对不完整，主要是由于缺乏沉积物补给，仅保存了最大洪泛面附近的沉积。
The tectonic activity in the Longmen Mountains exhibited notable phased changes in the Upper Triassic Xujiahean period.The deposition stages of the second and fourth members of the Xujiahe Formation coincided with the stages of thrusting in the Longmen Mountains.The depocenter and subsidence center of the western Sichuan foreland-like basin are located in the foredeep near the basin-margin thrust belt,and the reservoirs on both sides of the basin are well developed and their deposits are very asymmetric.As the downcutting erosion increased with enhancing tectonic activities in the Longmen Mountains orogen,the lowstand systems tract on the side of the basin-margin thrust is better developed,while the highstand systems tract is preserved incompletely because of later subaerial exposure and erosion.On the other hand,the side of the forebulge slope was marked by steady slow uplift and weak downcutting erosion,and so the lowstand systems tract is absent or not well developed and the highstand systems tract is better developed due to weaker erosion in the late stage.The deposition stages of the third and fifth members of the Xujiahe Formation coincided with the repose stage of thrusting in the Longmen Mountains.The depocenter and subsidence center of the western Sichuan foreland-like basin moved toward the forebulge;the deposits on both sides of the basin are less asymmetric,which are characterized by the development of regional caps and source rocks.The sequence filling patterns of the two stages are similar to those of the thrusting stages.However,their depositional sequences, especially the highstand systems tract,in the front of the orogen are completely preserved because of weaker tectonic erosion;whereas in the forebulge the sequences are relatively incomplete mainly owing to lack of supply of sediments and thus only the sediments near the maximum flooding surface are preserved.